NMR imaging method

Abstract

An NMR imaging method for measuring a magnetization distribution of an article under test, particularly the magnetization distribution including a longitudinal relaxation effect, by a Fourier imaging method with identification of polarity of the magnetization distribution. A homogeneous phantom is measured by the Fourier imaging method and image-reconstructed so that a reference image data which reflects a phase rotation inherent to an NMR imaging apparatus is obtained. Then, a magnetization distribution of an article under test is obtained in a similar measurement and image reconstruction sequence, and products of the reference image data and the image data of the article under test are stored as the signs to represent the polarity of magnetization of the article under test.

We claim: 
     
       1. An NMR imaging method comprising the steps of: (a) measuring a magnetization distribution of a homogeneous phantom by a first sequence of a Fourier imaging method, and storing real parts, imaginary parts or the signs thereof of image-reconstructed data thus measured into a first memory;   (b) measuring a magnetization distribution of an article under test by a second sequence of a Fourier imaging method and storing real parts, imaginary parts or the signs thereof and absolute values of image-reconstructed data thus measured into second and third memories, respectively; and   (c) multiplying at respective coordinates the real part, imaginary part, or the sign thereof, of the data stored in said first memory by the real part, imaginary part, or the sign thereof, of the data stored in said second memory, and storing the signs at the respective coordinates in said third memory as the signs of the image reconstructed data represented by the absolute values in said third memory.   
     
     
       2. An NMR imaging method according to claim 1 wherein the measurement of magnetization distribution of the article under test is a measurement of the magnetization distribution including a relaxation effect of magnetization. 
     
     
       3. An NMR imaging method according to claim 1 wherein said first sequence comprises the steps of applying a 90° R.F. pulse and a 180° R.F. pulse to obtain a spin echo, applying a first gradient magnetic field for phase encoding, and sampling a signal while a second gradient magnetic field orthogonal to the first gradient magnetic field is applied, and said steps of the first sequence are repeated a plurality of times with different strengths of the first gradient magnetic field. 
     
     
       4. An NMR imaging method according to claim 1 wherein said second sequence comprises the steps of applying a 90° R.F. pulse and a 180° R.F. pulse for obtaining a spin echo, applying a first gradient magnetic field for phase encoding, sampling a signal while a second gradient magnetic field orthogonal to said first gradient magnetic field is applied, and applying a second 180° R.F. pulse for reversing magnetization prior to the application of the 90° R.F. pulse, and said steps in the second sequence are repeated a plurality of times with different strength of said first gradient magnetic field. 
     
     
       5. An NMR imaging method according to claim 3 wherein said first memory stores therein real parts, imaginary parts or the signs thereof of data in an area along the direction of the second gradient magnetic field. 
     
     
       6. An NMR imaging method according to claim 3 wherein said first memory stores therein real parts, imaginary parts or the signs thereof of data on a line crossing a center of a view field along the direction of the second gradient magnetic field. 
     
     
       7. An NMR imaging method according to claim 2 further comprising the steps of: (d) measuring a second magnetization distribution image free of the relaxation effect of the magnetization of the article under test in said first sequence and storing absolute values of image-reconstructed data thus measured into a fourth memory; and   (e) calculating a distribution of a longitudinal relaxation time of the article under test by the data stored in said third and fourth memories and storing the resulting distribution into a fifth memory.   
     
     
       8. An NMR imaging method comprising the steps of: (a) measuring a magnetization distribution of a homogeneous phantom by a first sequence of a Fourier imaging method, and storing real parts, imaginary parts or the signs thereof of image-reconstructed data thus measured into a first memory,   said first sequence of a Fourier imaging method including the steps of:   repeatedly exciting spins of particles in said phantom,   applying a first gradient magnetic field for phase encoding after each step of exciting,   sampling a signal from said phantom while a second gradient magnetic field is applied after each step of applying the first gradient magnetic field, and   performing a Fourier transformation on data obtained by said step of sampling;   (b) measuring a magnetization distribution of an article under test by a second sequence of a Fourier imaging method and storing real parts, imaginary parts or the signs thereof and absolute values of image-reconstructed data thus measured into second and third memories, respectively,   said second sequence of a Fourier imaging method including the steps of:   repeatedly exciting spins of particles in said article, which suffer a relaxation effect within a predetermined time period,   applying said first gradient magnetic field for phase encoding after each time period,   sampling a signal from said article while said second gradient magnetic field is applied after said step of applying the first gradient magnetic field, and   performing a Fourier transformation on data obtained by said step of sampling; and   (c) multiplying at respective coordinates the real part, imaginary part, or the sign thereof, of the data stored in said first memory by the real part, imaginary part, or the sign thereof, of the data stored in said second memory, and storing signs of the products at the respective coordinates in said third memory as the signs of the image data represented by the absolute values in said third memory.